This invention relates to circuitry for gating a color burst signal in one aspect and to clamping the backporch portion of a video signal in another aspect. In a more specific aspect, circuitry for controlling the color burst gating and backporch clamping is provided.
The prior art suggests a color burst signal gating technique wherein a pulse signal coincident in time with the blanking portion of a video signal is applied to a resistor-capacitor integrating network. Therein was derived a gating signal which was employed to trigger an oscillator on, for the APC and ACC detectors during the color burst signal.
Although the above-mentioned technique has been and still is employed in numerous available color television receivers, it has been found that the attainable result does leave something to be desired. For example, it has been found that the width of a pulse signal available from such an integrating network tends to vary in accordance with variations in the loading of the circuitry. Moreover, it has also been found that such circuitry tends toward a relatively slow discharge whereupon chroma signals related to scene immediately following a color burst tend to gate in along with the burst signal because the gate undesirably trails off rather than abruptly ends.